Various embodiments of self-adhesive sheet-like structures are known, such as, for example, medical plasters. Skin plasters for medical purposes customarily have adhesive surfaces based on rubber resins or polyacrylates. The plasters having rubber adhesive surfaces have the disadvantage that residues, which are difficult to remove, remain on the skin when these plasters are removed again. In addition, these plasters frequently lead to skin irritation. The disadvantages of plasters having adhesive surfaces based on polyacrylates are the occasionally occurring skin reddening, which may progress to skin irritation, and the skin softening processes which are generally seen when there is inadequate access for air. These disadvantages appear particularly intense when polyacrylate adhesive surfaces remain on the skin for longer than one day, and when the surface covered by the adhesive is relatively large in extent.
Self-adhesive sheet-like structures which are used for industrial purposes and whose adhesive effect is based on polyvinyl chloride (PVC), (PVC being used either as an adhesive coating on a support material or as a self-adhesive film) have the disadvantage that an adequate adhesive effect is only achieved on smooth and even substrates. In addition, some of the low molecular weight plasticizers generally contained in PVC act, because of their chemical structure, as solvents and/or they are able to migrate into the substrates.
It has now been found that self-adhesive sheet-like structures which adhere well even to rough and uneven surfaces, can be removed again leaving virtually no residues and, in addition, are tolerated by the skin, are obtained by coating any desired support materials with a polyurethane reaction mixture which cures with the formation of a highly elastic gel of firm structure. Gels similar to those used in the present invention are disclosed in U.S. Pat. No. 4,456,642 including some gels which have a tacky gelatinous consistency. However, the disclosure does not teach that gels within its broad teaching could have utility as adhesive materials nor does it teach how to select gels within its broad teachings which have this property.